My Tempest "die" below 21Hz

Discussion in 'Archived Threads 2001-2004' started by Manuel Delaflor, Oct 7, 2002.

  1. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    I have a Tempest on a 220L sonotube tuned to 20Hz with a PE 300-794 (it is my first DIY project and I would like to say thanks again everyone on this forum for all the help).

    I have a Very nice flat response down to 21 Hz, but at this point it rolls of considerably. I got response to 17Hz but is down more than 10dB.

    If I change the rumble filter (I don't know how) or a bass boost (which is in the instructions sheet), do you think I will be able to get a flat response down to higher 10's?
     
  2. Patrick Sun

    Patrick Sun Moderator
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    What does it sound like when you actually listen to it when it's playing music and movie soundtracks?

    You're okay, your sub's okay, now go play!
     
  3. Mark_E_Smith

    Mark_E_Smith Second Unit

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    Dude, you are tuned to 20 Hz after that its going top fall off hard! Tis the nature of ported enclosures.
     
  4. Jack Gilvey

    Jack Gilvey Producer

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    A vented sub rolls off below Fb at 24dB/oct. Sounds like "dying" to me. [​IMG]
     
  5. Will Orth

    Will Orth Stunt Coordinator

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    Just a Question?? what are the lowest notes recorded on dvd movies? i have not felt anything below 25-30 hz, seems like there is a lot of hype on getting the lowest FQ where the program material does not exist, I used to be a recording engineer 12years back and the lowest note we recorded was about 38hz i know times have changed but all that recall low stuff is flutter and pure pressure on the driver- making it fail or die sooner than expected..

    Just a thought..

    Will
     
  6. Dustin B

    Dustin B Producer

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  7. Dave_Gib

    Dave_Gib Stunt Coordinator

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    Dustin B, that is about the coolest picture I have ever seen in my life, what and how much is it?
     
  8. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    I think they're from the SVS website, they must have gotten some new software toys to make those colorful waterfalls. [​IMG]
    SVS was the reason I built my sub... I salute them.
    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
  9. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    Oh, about Manuel trying to get response down to 17hz I think it's crazy. 20hz is on the brink of the audible spectrum as it is and he wants to risk pushing a tempest past the rumble filter protection? Heck, I didn't think it was even possible to get a smooth response to 21hz with a 220L sonotube @ 20hz.
    If you want more bass, perhaps test adding bass boost to the lower more audible notes.
    I think this could very well be a case of audiophilia bass nervosa. (Just playing) [​IMG]
     
  10. Dustin B

    Dustin B Producer

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    Tom V has done a whole bunch of these from various scenes in movies. You can find them in the FAQ section of the their website. Here is a direct link (note only the ones with * at the end are in color, the others were done on an older version of the software):
    http://www.svsubwoofers.com/faq.htm#moviedemos
    The software Tom used is SpectraPlus. How much it costs depends on what package you get. They also don't out right list the packages prices. Let us know the pricing if you decide to get it:
    http://www.spectraplus.com/
     
  11. Greg_R

    Greg_R Screenwriter

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    Location:
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  12. Craig Woodhall

    Craig Woodhall Supporting Actor

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    absolutely, you should hear my BPD1803 with a 15hz tone with 800 watts.. can't hear it, but it rattles all my internal organs [​IMG]
     
  13. David Hull

    David Hull Auditioning

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    Manuel,

    Your best bet to produce more low frequency sound is to lower the tuning of your enclosure and, ideally, to increase the size of the enclosure. Since the later might require a total rebuild, tuning the enclosure to a lower frequency, by increasing the port length, is going to be your best bet. However, there is a tradeoff. If you tune the enclosure lower without increasing its size, then you will lose some upper bass energy. Your best bet is to experiment by installing a port tuned to about 14 hz, then shorten it by a half inch at a time while listening to, or measuring the sub in between.

    Cheers,

    Dave
     
  14. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    First, thanks for all the replies.

    Patrick Sun

    You definitely have a point. I do enjoy it a lot just how it is. Thanks.

    Mark_E_Smith

    It is tuned at 20Hz but it falls dramatically from 21Hz. That is my point.

    Jack Gilvey

    I won't change the amplifier, sounds risky. I believe the one I have doesn't have any boost. But I don't know where is the rumble filter (in Hz), or if it is set at all.

    Chris Tsutsui

    I have several CD's with tube's Organs that can reach 16Hz. I want to be able to play that notes. You also mention the rumble filter. How can I know if my amp has one enabled? I believe it is flat, no boost version.

    Oh, and from 21Hz is really flat to the crossover point.

    Craig Woodhall

    Yes, that is what I want to achieve. Of course, to the possibilites of a Tempest in a 220L enclosure.

    David Hull

    I will play first with the tunning. I didn't wanted to tune lower in my design because the Frequency Response was not flat. Of course, I will count on some room gain.
     
  15. David Hull

    David Hull Auditioning

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    Manuel,

    In response to your response to Mark_E_Smith, don't forget that the tuning frequency is also the -3 dB frequency. So, even though you have the enclosure tuned to 20 Hz, it will start to roll off towards the F3 point, and to an eventual 24 dB per octave roll off, at about 30 Hz. If you want to hear the 16 Hz of a pipe organ, I would recommend tuning it to slightly below that frequency. The transfer function of your room should help flatten the overall response, as you said. Just make sure you turn the rumble filter off when playing music.

    Cheers,

    Dave
     
  16. Chris Tsutsui

    Chris Tsutsui Screenwriter

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    If I remember correctly the parts express amp has a built in rumble filter at like 20hz. In other words, it starts to filter out frequencies below 20hz from playing through your amplifier to prevent damage.
    The amps also has 0 decibels in boost at default unless you purchased a more expensive model 300-794 that features bass boost.
    The manual should have a chart that tells you to swap resisitors for the bass boost. This bass boost chart will tell you the Filter FC and Filter Q depending on the resisitors you added. The higher the frequency of the boost, the higher the Fc (corner frequency). Fc is also an indication of the frequency where the "rumble" filter starts to take affect.
    So say you want the sub to extend to 17hz... adding a 2db boost at 20-23hz region will result in a Filter Fc of 16hz.
    Maybe some experimentation with tuning and boost you could reduce the roll off slope a little. Or you can just blame the radio shack meter and compensation numbers for not displaying higher LF notes. [​IMG]
     
  17. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    David,
    Thanks for your input. But as Jacks points out later, just tune it lower would be useless with my actual amp settings.
    Chris,
    I finally found the info I needed on the manual (which I thought was lose). I need to do what you said, set a bass boost of 2dB's at 20-24Hz
    Jack,
    Those were my feelings also. It seemed to me that the amp, rather than the tune point, was my problem. I feel this is interesting, because it appears that most people just tune the sub and forget about the amp (and usually tune it lower than 20Hz), but as the link you give shows, the stock 300-794 is good to 20Hz but nothing lower.
    __________________
    To all, in case you wonder, here is a graph of my tempest FR. It is taken at my listening possition using the RS SPL Meter (without any correction) and Spectralab software. The 60Hz peak is an artifact and the 50Hz is a room mode (I have to live with it or destroy the imaging of my mains [​IMG] )
    http://us.f1.yahoofs.com/users/57b1b...xsUz9AiCak6Hz3
     
  18. Patrick Sun

    Patrick Sun Moderator
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    I don't "see" a problem.
     
  19. Manuel Delaflor

    Manuel Delaflor Supporting Actor

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    I found a site that explains what is happening and also gives "a cure":
    PE 300-794 modifications
    What do you all think about it? I'm specially concerned by the 12Hz rumble filter. Is at that frequency still a good protection for a Tempest?
     

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